1. Field of the Invention
The present invention relates to a thermal blanket and more particularly to a blanket which conditions the temperature of the trunk and head of a person by convection.
2. Related Prior Art
Every year thirty-five million patents in the United States and Europe will suffer from hypothermia if not properly treated. This condition has been treated using heated cotton blankets, warm water circulation blankets and mattresses, or infrared heating lamps. The material and labor costs for these products are significant. However, without this treatment the results can be discomfort, bleeding disorders, cardiac dysfunction and possibly death.
The most common method of warming a patient has employed a heated cotton blanket. The blanket, which is reusable, is preheated and then laid on the patient. After the blanket has dissipated its heat, it is used to cover another preheated blanket which is placed on the patient. This method of heating a patient requires a considerable amount of blanket preparation. Further, some people, such as diabetes patients, cannot tolerate the weight of a blanket on their feet. A more significant problem, however, is that the preheated blanket does not achieve a satisfactory result. Measurements have shown that the blanket does not heat the patient but simply acts as an insulation requiring the patient to produce the heat and warm himself.
A better mode of patient temperature control is provided by the circulating water blanket or mattress. Warmed water is circulated through tubes inside the blanket or mattress, to warm the patient. This structure provides heat to the patient. However, the results from the circulating water blanket are still not optimum. The small surface area in contact with the blanket results in minimal heat transfer. Also, since the blanket contacts the patient, its weight or the patient's weight, applies heat and pressure to the patient's skin, frequently resulting in burns.
A significant advance in the prevention and treatment of hypothermia was made in my coauthored U.S. Pat. No. 4,572,188, entitled "AIRFLOW COVER FOR CONTROLLING BODY TEMPERATURE". Improvements to the airflow cover disclosed and claimed in the '188 patent are found in the following co-pending, commonly assigned U.S. patent applications:
Ser. No. 07/703,592, filed May 20, 1991; and PA1 Ser. No. 07/887,233, filed May 19, 1992.
The patent and both of these patent applications are incorporated herein by reference. The latter incorporated U.S. patent application incorporates a foot drape into a convective thermal blanket. Commonly assigned U.S. Pat. 5,184,612, which is also incorporated by reference, describes a convective thermal blanket with an uninflatable, transparent upper body drape for covering the chest area and enabling viewing thereof. The airflow cover of the '188 patent and the thermal blanket of the incorporated U.S. applications and '612 patent comprise inflatable, self-erecting structures which cover a patient and exhaust warmed inflating air onto a covered patient. These products safely, and efficiently elevate and maintain patient body temperature. The fast and widespread acceptance of these products by the marketplace testifies to their effectiveness. Since 1988, over four million patients have been warmed by convective blankets manufactured according to the teachings of the '188 patent. These products are referred to as Bair Hugger.RTM. thermal blankets. Bair Hugger.RTM. is a trademark owned by Augustine Medical, Inc., the assignee of this patent application.
Since the introduction of Bair Hugger.RTM. products, a number of other inflatable, convective thermal blankets have been introduced into the marketplace. Such blankets operate in the same manner as the airflow cover described in the '188 patent; that is, they comprise an inflatable cover with multiple airflow paths and apertures which open through the bottom of the cover to exhaust warmed inflating air from the cover onto a patient. Hereinafter, these products are referred to as "Augustine-type" convective thermal blankets.
Some very important comparisons have been made between Augustine-type convective thermal blankets and prior art non-convective devices. See, for example, D. I. Sessler, M.D., et al., "Skin-Surface Warming: Heat Flux and Central Temperature", in ANESTHESIOLOGY, Vol. 73, p-218-224, 1990 and J. M. Hynson, M.D., et al, "Intraoperative Warming Therapies: A Comparison of Three Devices". Journal of Clinical Anesthesiology, Vol. 4, p-194-199, 1992.
One significant omission in the design and operation of prior art thermal blankets of the Augustine type is that they provide no way to control heat loss or gain through a patient's head. The head, like the core or trunk of a patient's body, is one of the areas of the greatest heat loss or gain. It would therefore be desirable to provide a single means and mode of treatment which would actively warm the head of the patient as well as the rest of the body. A cap for heating a patient's head is described in the '188 patent. However, this head heating device is separate from the airflow cover described in the patent and requires a separate hose attachment. It would be desirable to heat both the head and chest areas with a single convective thermal blanket of the Augustine type.